Condensed Financial Information (Parent Company) (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Expense [Abstract]
Total interest expense	$ 871	$ 975	$ 815
Parent Company [Member]
Interest Expense [Abstract]
Total interest expense	985	1,007	882
Parent Company [Member] | Long-term Debt [Member]
Interest Expense [Abstract]
Total interest expense	779	806	689
Parent Company [Member] | Long-term Debt [Member] | Affiliated Entity [Member]
Interest Expense [Abstract]
Total interest expense	28	16	15
Parent Company [Member] | Secured Debt [Member]
Interest Expense [Abstract]
Total interest expense	42	43	44
Parent Company [Member] | Junior Subordinated Debt [Member]
Interest Expense [Abstract]
Total interest expense	134	134	134
Parent Company [Member] | Stock Purchase Contracts [Member]
Interest Expense [Abstract]
Total interest expense	$ 2	$ 8	$ 0